Microbiology · Year 2 · from Microbiology
Case 1: Cerebral Malaria
Presentation
A 32-year-old woman presents with high fever, severe headache, and altered mental status. She returned 10 days ago from a 3-week trip to rural Kenya where she was doing volunteer work. She took mefloquine prophylaxis but admits to missing several doses. She has had 4 days of fever with rigors and now cannot be roused easily. Vital signs: temperature 40.2°C, heart rate 120 bpm, blood pressure 90/60 mmHg. She opens her eyes to voice but is disoriented and follows commands inconsistently. Peripheral blood smear shows intraerythrocytic ring forms with multiple rings per cell and parasitemia of 15%. Rapid diagnostic test is positive for Plasmodium falciparum.
Clinical Image
Peripheral blood smear demonstrating Plasmodium falciparum infection with characteristic small ring forms, multiple rings per red blood cell, and high parasitemia - features associated with severe malaria.
Image Source: Lecture image - malaria parasitology
Questions
- What is the diagnosis, and which Plasmodium species is responsible?
- Why is this species associated with severe disease, particularly cerebral malaria?
- What is the appropriate management for severe malaria?
- How could this case have been prevented?
Answers
- Diagnosis and species: This is severe malaria with cerebral involvement caused by Plasmodium falciparum. The diagnosis is based on travel to an endemic area, fever with altered consciousness, and peripheral smear showing P. falciparum (characterized by small ring forms, multiple rings per RBC, and high parasitemia). P. falciparum causes the vast majority of malaria deaths and is the only species that commonly causes cerebral malaria.
- Why P. falciparum causes severe disease: P. falciparum has unique pathogenic features:
- Cytoadherence: Infected RBCs express PfEMP1 surface protein that binds to endothelial receptors (ICAM-1, CD36), causing sequestration in microvasculature
- Cerebral malaria: Sequestration in cerebral capillaries causes microvascular obstruction, hypoxia, and blood-brain barrier disruption
- High parasitemia: Unlike other species that prefer reticulocytes or older RBCs, P. falciparum invades RBCs of all ages, enabling massive parasite loads
- Rosetting: Infected RBCs adhere to uninfected RBCs, worsening obstruction
- No hypnozoite stage (unlike P. vivax and P. ovale), but severe acute illness
- Management of severe malaria:
- Intravenous artesunate is the treatment of choice (superior to quinine)
- Dose: 2.4 mg/kg IV at 0, 12, 24 hours, then daily until oral therapy tolerated
- Exchange transfusion considered for parasitemia >10% with severe disease
- Transition to oral artemisinin-combination therapy (ACT) when able
- Supportive care: ICU monitoring, seizure prophylaxis if cerebral involvement, correct hypoglycemia, treat secondary infections
- Monitor for delayed hemolysis after artesunate therapy
- Prevention strategies:
- Chemoprophylaxis adherence: This patient's missed doses likely contributed to breakthrough infection. Options include atovaquone-proguanil (Malarone), doxycycline, or mefloquine depending on resistance patterns
- Mosquito avoidance: DEET-containing repellents, permethrin-treated clothing and bed nets, avoiding outdoor exposure at dusk/dawn (peak Anopheles feeding)
- Awareness: Seek medical attention for any fever within 3 months of travel to endemic area
- Prophylaxis must be continued after leaving endemic area (duration varies by drug)